In recent years, the gold nanomaterial assemblies with specific shapes possess unique properties which are different from those of monodisperse gold nanomaterials and gold materials, making them extremely bright prospect. Therefore, the self-assemblies of gold nanomaterials attract widespread attentions of nano-scientists around the world. Gold nanomaterials mainly include gold nanoparticles and gold nanorods. These nanomaterials possess specific optical absorption, light scattering and Raman enhancement effects depending on the size and shape, which make these two nanoparticles the most widely used materials in the nanoscience and nanotechnology research field, especially the gold nanorods.
A single gold nanorod has two localized surface plasmon resonance peaks, which are a longitudinal plasmon resonance peak (near infrared or infrared region) and a transverse plasmon resonance peak (around 520 nm), due to the two resonant directions of conduction band electrons on the rod. And gold nanorods, with spatial geometry and chemical anisotropy, can achieve strong light absorptions in the visible or near infrared region by adjusting the aspect ratio of gold nanorods (the ratio of length to diameter of the gold nanorods). Theses unique properties make gold nanorods to be the excellent raw material for the controllable self-assembly, and then provide a good model for theoretical analysis of the self-assembly materials. Thus the physical and chemical properties of macroscopic materials can be better understood by studying nature of the controllable, dynamic self-assembled materials. Notably to mention, the spatial geometry and chemical anisotropy are the key factors for the nanomaterials to achieve controllable self-assembly.
Janus particle was proposed by De Gennes in 1991 for the first time in the Nobel award ceremony, in order to describe a particle with different spherical nature. The difference of this nature is mainly due to the different spherical geometry of the particle. And Janus particle now attracts extensive attention of the scientific community, due to its unique asymmetric structure and properties, making it strong application prospects. Recently, the preparation methods of Janus particle are mainly including microfluidic surface modification synthesis, topology selection, the template self-assembly synthesis, controllable phase separation, and controllable surface nucleation. Self-assembly of gold nanomaterials has very strong plasmon coupling effects, leading to the strong electromagnetic enhancements. And binary plasmonic self-assemblies show fascinating properties different from that of the two separate nanomaterials, really makes the assembly of nanoparticles Janus wonderful and brilliant. Surprisingly, there is no reported method that successfully achieve high-yield binary nanoparticle Janus assemblies yet. Therefore, it is particularly important to establish a method to obtain high-yield binary nanoparticles Janus assemblies.